1. Field of the Invention
The present invention generally relates to an apparatus in which an analog video signal is converted into a digital signal and the thus obtained digital signal is recorded in a recording medium by utilizing magnetism, light, or the like, and particularly relates to an apparatus in which digital dubbing of a reproduced signal in the above-mentioned apparatus is preferably carried out.
2. Description of the Prior Art
As such an apparatus in which an analog video signal is converted into a digital signal so as to be recorded in a recording medium by utilizing magnetism, light, or the like, for example, digital VTRs are widely used. Digital VTRs are featured in that it is possible to perform recording/reproducing with less deterioration in picture quality in comparison with conventional analog VTRs, and specifically, in that a signal-to noise ratio (S/N) is not lowered. That is, although the S/N is reduced at the rate of 20.multidot.log n [dB] when dubbing is carried out n times in the conventional analog VTR, such a reduction as effected in the conventional analog VTR is not generated in the digital VTR.
When a video signal is converted into a digital signal, for example, in the digital VTR, the thus obtained digital signal is a high speed data having a data rate of about 100 Mb/second or more, and therefore it is exceedingly difficult to record such a high speed data, for example, by using a single magnetic head. In order to cope with such a problem, used is a technique that the digital signal is distributed into a plurality of channels so as record the thus distributed signals simultaneously by using a plurality of magnetic heads.
In order to perform distribution of a digital video signal, the following methods are known as described, for example, in an article by Hirano et al., entitled "A study on Variable-Speed Reproduction of the Digital VTR", SMPTE Journal, Vol. 92, No. 6, June 1983 pp 636-641. In this method, a data of a video signal corresponding to every picture element is converted into a digital signal of n bits and the thus obtained digital signals are distributed into three channels A, B, and C in such a manner as follows (hereinafter, a digital signal of n bits corresponding to one picture element is referred to as "a picture element signal").
1. For every picture element signal, upper bits of digital signal, middle bits of digital signal, and lower bits of digital signal are distributed into channels A, B, and C respectively.
2. The digital signals are successively distributed for every picture element signal into A, B, C, A, B, C, . . . , in order.
3. A picture element signal corresponding to a portion at the left side of a screen, a picture element signal corresponding to a portion at the center of the same, and a picture element signal corresponding to a portion at the right side of the same are distributed into channels A, B, and C respectively.
In the foregoing article, however, consideration is made mainly about the distribution for a signal, such as an NTSC signal, in which a luminance signal and a chrominance signal are combined by frequency division multiplex, that is, a so-called composite signal.
Further, the digital VTR has such a feature that dubbing can be carried out with less deterioration in picture quality, that is, with a high picture quality, and therefore the digital VTR is employed for use in studio, in business, etc. Moreover, the digital VTR is expected for use in a high definition television which requires a higher picture quality in comparison with the present television system (in the high definition television the number of scanning lines is selected to be about twice as many as that of the present television system so as to realize high definition). In order to perform recording with such a high picture quality as described above, it is more preferable to use a component method in which a luminance signal and a chrominance signal are processed separately from each other, than the use of the foregoing composite signal. According to the component method, three primary color signals (for example, an R signal, a G signal and a B signal) constituting a video signal are converted into a luminance signal Y and two kinds of chrominance signals I and Q (in the case of a high definition television, a luminance signal Y and chrominance signals C.sub.W and C.sub.N), and recorded separately from each other. In this case, a sufficient visual quality can be obtained even if a signal band of the chrominance signals C.sub.W and C.sub.N is selected to be about 1/3-1/4 times as much as that of the luminance signal Y.
However, there have been no reference in which reference is made to the optimization of distribution of digital signals in such a component method, and it is a matter of course that there have been no references in which reference is made to a method of performing digital dubbing of a reproduced signal in such a component method.